In cellular wireless systems, such as Long Term Evolution (LTE) and New Radio (NR) standards in the Third Generation Partnership Project (3GPP), resources for uplink (UL) transmissions are normally scheduled by a network node (eNB or gNB). This can be done dynamically, i.e., the eNB schedules the UL transmission per transmission time interval (TTI). Alternatively, this can be done using a semi-persistent scheduling (SPS) framework, so that multiple TTIs are granted at the same time, i.e., prior to a data transmission, where UL transmissions are scheduled without a dynamic grant. Configuration of SPS includes periodicity of the grant, allocation and modulation and coding scheme (MCS) in subsequent SPS occasions.
Another related concept in wireless transmission is data retransmission. When the transmission of data fails due to some errors in the channel that cannot be fixed in the decoding, the receiver may ask the transmitter for data retransmission. The retransmission method may simply be transmitting the same data or a better coded data, with lower rate, etc. At the receiver side, the receiver may simply use the new, retransmitted, data instead of the old one or combine them to make a more reliable detection. This is the basis of Hybrid Automatic Repeat Request (HARQ).
LTE uses a synchronous HARQ concept where acknowledging of correctly received data or acknowledging of an erroneous detection (ACK/NACK) has to be sent by the receiver of data at a certain time in a Physical Hybrid-ARQ Indicator Channel (PHICH). In LTE, the wireless device (wireless device) uses the same HARQ process number every 8 TTIs. Retransmission of the data, if needed, with the same HARQ happens every 8 TTIs. Since the wireless device uses a specific HARQ process identification (ID) at a specific subframe, the eNB knows exactly which HARQ is received and when it is received.
The NR standard that is being specified in 3GPP is based on asynchronous HARQ transmission, which means that there is no certain time that is expected for ACK/NACK, i.e., PHICH will not be introduced. Moreover, in LTE sTTI and in reduced processing time (n+3), PHICH is not introduced and therefore no ACK/NACK is transmitted.
SPS (the term in LTE) is the same as “UL transmission without UL grant—type 2” that is being discussed in 3GPP. The other “UL transmission without UL grant—type 1” is different only in the resource configuration. Since the final terminology has not been settled yet, in this disclosure, SPS is used to refer to both LTE SPS and NR “UL transmission without UL grant” type 1 and type 2, or ‘configured grant’ which corresponds to an uplink transmission without a dynamic grant.